Conventional apparatus utilized in the cable and wire insulating industry includes an insulation extruder which melts a plastic compound that is to form the insulation, for ultimate deposition of the insulation around the cable or wire to provide the final insulated cable or wire product. Actual coating is accomplished by a tubular mandrel through which the cable is fed, and having a guider tip which cooperates with a forming die. Molten insulation flows over the guider tip between the guider tip and the forming die to evenly coat with insulation the cable passing through the tubular mandrel. A capstan, or like structure, pulls the cable off a payoff spool, and pulls it through the tubular mandrel, the insulated cable ultimately being wound up on a take-up spool.
As long as the cross-sectional dimensions of the cable are uniform (e.g., the cable has a constant diameter) the apparatus described above works well. However, if the bare cable is damaged or poorly constructed, there may be portions thereof that have significantly larger cross-sectional dimensions than the average cross-sectional dimension. If such an oversized portion is pulled through the cable insulating apparatus, it can break the guider tip.
According to the present invention, it has been recognized that guider tip breakage may occur as a result of cable portions having too large a cross-sectional dimension being pulled through the guider tip, and according to the present invention, a method and apparatus are provided which can avoid guider tip breakage (and like adverse consequences) that may result from a cable having too large cross-sectional dimensions. This is accomplished according to the present invention by sensing the cross-sectional dimensions of the bare cable as it is fed to the tubular guide mandrel, and generating a signal in response to the cable sensing if any cross-sectional dimension of the cable is greater than a predetermined amount. The generated signal may provide for automatic shut down of the extruder and the capstan, and/or may activate an alarm or bring components into play which will automatically even out the too-large cross-sectional dimension of the cable.
The apparatus for sensing the cross-sectional dimensions of a cable in accordance with the present invention includes a housing and a sensing member. The housing has first and second opposite open ends and defines an open volume between the first and second open ends. The sensing member has a conically shaped aperture formed therein, and the housing walls or like means are provided for mounting the sensing member for guided slidable movement within the housing open volume in the dimension from the first end to the second end thereof, and so that the conically shaped aperture tapers from the first end of the housing to the second end thereof and is in-line with the openings in the housing first and second ends. A stop member is associated with the housing first end for stopping movement of the sensing member, and spring biasing means act between an annular shoulder in a central interior portion of the housing and the sensing member to bias the sensing member into engagement with the stop member.
The apparatus according to the invention also includes means for mounting a signal generating means in the operative path of slidable movement of the sensing member. For instance, the housing may have a slit formed therein extending in the dimension of slidable movement of the sensing member, and the sensing member may have an actuator extending outwardly therefrom through the slit. With the signal generating means mounted adjacent the slit, the actuating member will move into operative engage with the signal generating means when the sensing member is moved against the bias of the spring means.
It is the primary object of the present invention to provide a method and apparatus for forming insulated cable from bare cable without destruction of the guider tip by sensing the cross-sectional dimensions of the bare cable being fed to the guider tip. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.